AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Well that could be your problem right there
Calling on Holley carb experts!!!!!!!!
- Thread starter duster360
- Start date
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Which part? Or all of it?
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,807
- Reaction score
- 13,113
Hyup part or all of it.
Questions
>Do you have a working,properly plumbed PCV?
>With the Vcan hooked up fulltime like that, is your idle timing 20*?
>What made you chose 20*?
>What is your idle rpm, and how much does it drop going into gear?
>How much does your vacuum drop when you drop it into gear?
> At what rpm is 34* achieved?
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I have a X brand pcv that I have read here works well.
Idle timing is definitely 20*
Seems to like it there. Started at 10* and the more I turned it the higher the idle got. Starts well too.
Manual transmission
34* at 3200 rpm
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,807
- Reaction score
- 13,113
Here is a summarry of where we are at;
If you read,and applied, my earlier post,we might not be still having this conversation.
OK, that's harsh, I'm sorry
But let's see what is going on:Why is your idlespeed 900rpm and your vacuum 11ish?
I'll tell you why, because it doesn't like to idle any slower right?...Why is that?
Because it is running at 20* idle timing, with slightly cracked secondaries , and tons of fuel .
And why 900? It's a manual trans and you can easily idle it at 750, maybe less,because you don't have an rpm drop going into gear.
And all your adjustments have conspired to make 900 about the minimum.
Ok so if, IF we wanted to idle that 275* cam at a more sane say 750rpm,how would we do that? We can't back out the speed screw, cuz it is already too far out, which being at square T-port exposure. So then all we have left is air and timing. We cannot take away air, because the beast is already borderline smoking black. What's left? That's right;timing.
But, you say, then my engine will not be as snappy!
Hey riddle me this; what is the slowest speed your 400hp monster will drive, before it gets all jumpy and you have to put the clutch in for fear it will bust a U-joint? Why does it do that? Because the power pulses are so strong is why. And they are so strong because of the 20* of idle-timing.
So you can kill two birds with one stone, by giving up some idle-timing.
So that takes me to what I said earlier, back it up to 14 max..... for now, and we'll fix the power timing later after the initial is fixed.
So the first thing to do is to disconnect the V-can and plug the port it was hooked to, and to crank the D to 12/14.
So read the rest of this novel, before you get started.
Ok so I'm gonna assume the timing is now 12 to 14.
What happened to the idle? Yeah I bet it hardly wants to stay running. So since your T-port is square, which is not enough anymore, crank in the speed screw 1.5 turns, close the secondaries completely and shut off the rear fuel, and open the fronts to 1.5. In my experience your cam does not require help from the secondary side. Awright start it up.
>>Click-vrooom,rumpidy-rumpidy-rumpidy; that is what it should sound like at 700, and that is how it should start......... because all the air entering he engine is now controlled by the primaries, and it all has to come by the T-ports, where it all picks up some fuel, in proportion to how much is flying by the throttles.
Ok so what has happened to the idle vacuum? Yeah it took a dump and is now in the neighborhood of 9/10inches; so what! Ok adjust the front idle mixture screws for best quality idle. If you can't get there between .5 and 1.5, then we have to adjust the T-port exposure until it falls in the range; remember the Mixture screws are just idle enrichment trimmers; the T-port is THE slow-speed fuel supply. So if 1.5 is not enough, then add T-port. If .5 is too much, subtract T-port. But do not wander too far from the T-port being "slightly taller than wide, which is where I baselined you when I said add 1.5 turns to the speed screw. If, I say IF, you cannot get a stable 750 idle using the primary systems then you have to ask the question why.
>Your 275* cam should not need help from the secondary side.
But I admit some 275s act more like 292s at idle, so maybe yours is one of those. So then the first thing you wanna do is verify the wet fuel level is correct and stable, forget fuel pressure. Fuel pressure is just a tool to maintain the wet fuel level; the carb at idle don't care about pressure, as long as the wet level is correct and stable.
Ok so assuming that passed..........
Now is the time to dick with the rear screws.
First reset the front mixture screws to the center of their range ,say 3/4 turn on Holleys. If you dicked with the speed screw, put it back to square plus 1.5 turns. If the idle speed is below 700, add timing until it gets there, but no more than 16*.
Now figure out if the engine wants more or less fuel. I do this by jamming a rag into the secondary side, which should make zero idle speed difference. And then I begin to cover the primaries, a little atta time. Sooner or later one of two things is gonna happen; the idle will go up, or it will go down. If it goes down, the engine wants more air...... or less fuel. If it goes up, the engine wants less air.... or more fuel.
>Take the rag out,and give her what she wants. At this point if she wanted air,kindof normal for a bigger than 275 acting cam, then crack the secondaries a tad.But keep in mind adding secondary air causes a chain reaction. The idle speed usually goes up, and this usually makes the back cylinders go lean, and makes for a really stinky, burns-your-eyes-stinky, exhaust, so you will have to add a little fuel to it; just a little. And so now the end result is a faster idle........ and here comes the chain reaction; so then you back out the speed screw........... which closes the T-port exposure, and so then the mixture gets screwed up and the immediate bandaid is to crank in more timing cuz everybody knows more timing is the best thing since sliced bread....... DON'T BELIEVE IT! This works for racecars and autos with hi-stall TCs that do not need to pull from 1000 rpm to 2500rpm; they can get away with thatchit--------
your M/T cannot. Because your M/T is gonna spend a large part of it's life at those rpms, and the smaller your rear gear, the more time it will be. Anyway, end of that rant.
Now revisit the front screws to see if they are still in the range of .5 to 1.5. And target 3/4 turn. and by now she should be running like a champ.
Ok shut it off, wait 5 seconds, and hit the key; don't touch the gas. If you got it right, 2 out of 3 times it will start like an old 289/302, namely click-vroom, rumpidy-rumpidy-rumpidy.
If I'm right, and if your 275*cam has unusually long ramps, as some do, from advertised to intake-actually-closed,then:
Your T-port exposure will now be a little taller than wide,and;your timing will now be 14/16,and; the front screws will be 3/4 turn,and; the secondaries barely cracked with no more than 1/2 turn on the screws, and the idle speed should be 750 plus/minus 50ish.
Now, put your left foot on the brake and your right on the clutch,OK I'm kidding, put your feet on the sideways pedals, and Start it up; click-vroom, declutch put it in second gear and slowly feed her clutch, letting the Rs come down; rumpidy-ruumppidy-ruuuuummppidddy, stall.What was the slowest speed it would stay running at.Was it 550 to 600? Start it back up, repeat but hold it at the lowest stable rpm for say 5 seconds. Is it stable there? yes? Ok good!Shut it off, Hook the Vcan up to the SPARKPORT, and we're done!
Well not quite, there is still the matter of recurving the D to again achieve a reasonable Power-timing, Speeding up the rate of advance to compensate for the loss of Vcan-timing, and tuning the Vcan for driveability.
_________________
The above assumes;
there are no vacuum leaks, the PV is not leaking, the fuel level is stable, the engine temp is pushing 195 and is stable there, all the fuel going into the engine is controlled by the low-speed circuit, and all the air that is entering the engine is controlled by the throttle valves, with a bit from the PCV. That the ignition system is up to the task, that the plug gaps are at least .035 ( I prefer .045 and a SuperCoil), and that the plug wires are doing what they are supposed to be and nothing else, and most importantly; that the valves are opening and closing, especially closing, at the appropriate and specified times.
BTW, your PV should be around 9.5 to 10.5,for best driveability
NOT 11/2=5.5 and NOT 10 less 2 =8 or any other nonsense you might have run across. With the new settings as above,IMO a 10.5 will be pretty close, with a 8.5 as a minimum.
How to know for sure? Take it for a ride with a PV plug installed, and a vacuum gauge stuck on the windshield. Get it into second gear,at a vacuum up near 16/ 18 and do a few throttle roll-ons, watching the gauge, and feeling the engine. When it lays down catch the vacuum reading. repeat at various speeds. I bet it lays over around 10.And so a 10 is what it wants.
BTW2, Guess what happens when you put the air cleaner back on and close the hood. NOTHING GOOD that's for sure. In a few seconds your beast is gonna react to that hot,hotter very hot underhood air and screw everything up that you just spent 2 hours perfecting.
I can't help you with your next decision, cuz it took me a couple of years to sacrifice my pristine hood.
OK,so............................ Happy HotRodding.
If you read,and applied, my earlier post,we might not be still having this conversation.
OK, that's harsh, I'm sorry
But let's see what is going on:Why is your idlespeed 900rpm and your vacuum 11ish?
I'll tell you why, because it doesn't like to idle any slower right?...Why is that?
Because it is running at 20* idle timing, with slightly cracked secondaries , and tons of fuel .
And why 900? It's a manual trans and you can easily idle it at 750, maybe less,because you don't have an rpm drop going into gear.
And all your adjustments have conspired to make 900 about the minimum.
Ok so if, IF we wanted to idle that 275* cam at a more sane say 750rpm,how would we do that? We can't back out the speed screw, cuz it is already too far out, which being at square T-port exposure. So then all we have left is air and timing. We cannot take away air, because the beast is already borderline smoking black. What's left? That's right;timing.
But, you say, then my engine will not be as snappy!
Hey riddle me this; what is the slowest speed your 400hp monster will drive, before it gets all jumpy and you have to put the clutch in for fear it will bust a U-joint? Why does it do that? Because the power pulses are so strong is why. And they are so strong because of the 20* of idle-timing.
So you can kill two birds with one stone, by giving up some idle-timing.
So that takes me to what I said earlier, back it up to 14 max..... for now, and we'll fix the power timing later after the initial is fixed.
So the first thing to do is to disconnect the V-can and plug the port it was hooked to, and to crank the D to 12/14.
So read the rest of this novel, before you get started.
Ok so I'm gonna assume the timing is now 12 to 14.
What happened to the idle? Yeah I bet it hardly wants to stay running. So since your T-port is square, which is not enough anymore, crank in the speed screw 1.5 turns, close the secondaries completely and shut off the rear fuel, and open the fronts to 1.5. In my experience your cam does not require help from the secondary side. Awright start it up.
>>Click-vrooom,rumpidy-rumpidy-rumpidy; that is what it should sound like at 700, and that is how it should start......... because all the air entering he engine is now controlled by the primaries, and it all has to come by the T-ports, where it all picks up some fuel, in proportion to how much is flying by the throttles.
Ok so what has happened to the idle vacuum? Yeah it took a dump and is now in the neighborhood of 9/10inches; so what! Ok adjust the front idle mixture screws for best quality idle. If you can't get there between .5 and 1.5, then we have to adjust the T-port exposure until it falls in the range; remember the Mixture screws are just idle enrichment trimmers; the T-port is THE slow-speed fuel supply. So if 1.5 is not enough, then add T-port. If .5 is too much, subtract T-port. But do not wander too far from the T-port being "slightly taller than wide, which is where I baselined you when I said add 1.5 turns to the speed screw. If, I say IF, you cannot get a stable 750 idle using the primary systems then you have to ask the question why.
>Your 275* cam should not need help from the secondary side.
But I admit some 275s act more like 292s at idle, so maybe yours is one of those. So then the first thing you wanna do is verify the wet fuel level is correct and stable, forget fuel pressure. Fuel pressure is just a tool to maintain the wet fuel level; the carb at idle don't care about pressure, as long as the wet level is correct and stable.
Ok so assuming that passed..........
Now is the time to dick with the rear screws.
First reset the front mixture screws to the center of their range ,say 3/4 turn on Holleys. If you dicked with the speed screw, put it back to square plus 1.5 turns. If the idle speed is below 700, add timing until it gets there, but no more than 16*.
Now figure out if the engine wants more or less fuel. I do this by jamming a rag into the secondary side, which should make zero idle speed difference. And then I begin to cover the primaries, a little atta time. Sooner or later one of two things is gonna happen; the idle will go up, or it will go down. If it goes down, the engine wants more air...... or less fuel. If it goes up, the engine wants less air.... or more fuel.
>Take the rag out,and give her what she wants. At this point if she wanted air,kindof normal for a bigger than 275 acting cam, then crack the secondaries a tad.But keep in mind adding secondary air causes a chain reaction. The idle speed usually goes up, and this usually makes the back cylinders go lean, and makes for a really stinky, burns-your-eyes-stinky, exhaust, so you will have to add a little fuel to it; just a little. And so now the end result is a faster idle........ and here comes the chain reaction; so then you back out the speed screw........... which closes the T-port exposure, and so then the mixture gets screwed up and the immediate bandaid is to crank in more timing cuz everybody knows more timing is the best thing since sliced bread....... DON'T BELIEVE IT! This works for racecars and autos with hi-stall TCs that do not need to pull from 1000 rpm to 2500rpm; they can get away with thatchit--------
your M/T cannot. Because your M/T is gonna spend a large part of it's life at those rpms, and the smaller your rear gear, the more time it will be. Anyway, end of that rant.
Now revisit the front screws to see if they are still in the range of .5 to 1.5. And target 3/4 turn. and by now she should be running like a champ.
Ok shut it off, wait 5 seconds, and hit the key; don't touch the gas. If you got it right, 2 out of 3 times it will start like an old 289/302, namely click-vroom, rumpidy-rumpidy-rumpidy.
If I'm right, and if your 275*cam has unusually long ramps, as some do, from advertised to intake-actually-closed,then:
Your T-port exposure will now be a little taller than wide,and;your timing will now be 14/16,and; the front screws will be 3/4 turn,and; the secondaries barely cracked with no more than 1/2 turn on the screws, and the idle speed should be 750 plus/minus 50ish.
Now, put your left foot on the brake and your right on the clutch,OK I'm kidding, put your feet on the sideways pedals, and Start it up; click-vroom, declutch put it in second gear and slowly feed her clutch, letting the Rs come down; rumpidy-ruumppidy-ruuuuummppidddy, stall.What was the slowest speed it would stay running at.Was it 550 to 600? Start it back up, repeat but hold it at the lowest stable rpm for say 5 seconds. Is it stable there? yes? Ok good!Shut it off, Hook the Vcan up to the SPARKPORT, and we're done!
Well not quite, there is still the matter of recurving the D to again achieve a reasonable Power-timing, Speeding up the rate of advance to compensate for the loss of Vcan-timing, and tuning the Vcan for driveability.
_________________
The above assumes;
there are no vacuum leaks, the PV is not leaking, the fuel level is stable, the engine temp is pushing 195 and is stable there, all the fuel going into the engine is controlled by the low-speed circuit, and all the air that is entering the engine is controlled by the throttle valves, with a bit from the PCV. That the ignition system is up to the task, that the plug gaps are at least .035 ( I prefer .045 and a SuperCoil), and that the plug wires are doing what they are supposed to be and nothing else, and most importantly; that the valves are opening and closing, especially closing, at the appropriate and specified times.
BTW, your PV should be around 9.5 to 10.5,for best driveability
NOT 11/2=5.5 and NOT 10 less 2 =8 or any other nonsense you might have run across. With the new settings as above,IMO a 10.5 will be pretty close, with a 8.5 as a minimum.
How to know for sure? Take it for a ride with a PV plug installed, and a vacuum gauge stuck on the windshield. Get it into second gear,at a vacuum up near 16/ 18 and do a few throttle roll-ons, watching the gauge, and feeling the engine. When it lays down catch the vacuum reading. repeat at various speeds. I bet it lays over around 10.And so a 10 is what it wants.
BTW2, Guess what happens when you put the air cleaner back on and close the hood. NOTHING GOOD that's for sure. In a few seconds your beast is gonna react to that hot,hotter very hot underhood air and screw everything up that you just spent 2 hours perfecting.
I can't help you with your next decision, cuz it took me a couple of years to sacrifice my pristine hood.
OK,so............................ Happy HotRodding.
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